Many of our hosted sites will use an SSL certificate to protect FTP. If your site uses SSL then your FTP client may be storing an old certificate and preventing you from accessing or changing your site. Here is how to delete an old Certificate in CoreFTP:
1. In CoreFTP. click "Manage" and then select "SSL/SSH Certificates"
2. Click on the certificate for the site that is giving you trouble.
3. Click Delete.
4. Click Ok.
Restart CoreFTP and reconnect to your site. You will be prompted to accept the new certificate.